Speaker John A. Boehner (R-Ohio) said Friday that he would form a House select committee to investigate the September 2012 attack on a U.S. diplomatic outpost in Benghazi, Libya.

At the same time, Rep. Darrell Issa (R-Vista), chairman of the House Oversight Committee, subpoenaed Secretary of State John F. Kerry to testify before another panel over the issue, which continues to drive conservatives before the midterm elections.

Boehner said he had little choice but to begin a House investigation after the State Department released a previously undisclosed email showing that a top White House aide had coordinated talking points about the attack for then-U.S. Ambassador to the U.N. Susan Rice.

"The administration's withholding of documents — emails showing greater White House involvement in misleading the American people — is a flagrant violation of trust," Boehner said. He said he expected the committee "to work quickly to get answers for the American people."

Questions about the White House's role in the early explanations of the attack at the U.S. outpost in Benghazi have continued to swirl, especially among conservative Republicans in Congress. The attack left four Americans dead, including Ambassador J. Christopher Stevens.

White House spokesman Jay Carney said earlier this week that the email was not previously released because it did not deal specifically with Benghazi, but with the broader unrest.

But a senior GOP leadership aide said Boehner “was furious to learn that the administration withheld relevant documents from a congressional subpoena.”

At the same time, Issa said the State Department's "disturbing disregard" for complying with the congressional investigation launched under Kerry's predecessor, Hillary Rodham Clinton, left him little choice but to subpoena Kerry's testimony.

Ben Rhodes, Obama’s deputy national security advisor, wrote the email to help prepare Susan...

"The department is not entitled to delay responsive emails because it is embarrassing or implicates the roles and actions of senior officials," Issa said Friday.

The hard-charging chairman has pursued an ongoing probe of the attack, but Democrats, too, especially those in tough reelection battles have begun to raise questions about the issue.

The recently disclosed email from Ben Rhodes, Obama's deputy security council advisor, urged Rice to describe the attack as the result of anti-American protests rather than a "broader failure of policy."

Republicans seized on the email as a "smoking gun," saying it shows that the White House sought to cover up the terrorist attack for political purposes.